The present invention relates to semiconductor processing, and more specifically, to methods and apparatus for substrate processing with improved throughput and yield. In some specific embodiments, the invention is particularly useful for forming titanium-containing films such as titanium nitride at heater temperatures of greater than about 400.degree. C. Such films may be used as patterned conductive layers, plugs between conductive layers, diffusion barrier layers, and adhesion layers. In addition, other embodiments of the present invention may be used, for example, to deposit other types of metal films, to alloy substrate materials, and to anneal substrate materials.
One of the primary steps in fabricating modern semiconductor devices is forming various layers, including dielectric layers and metal layers, on a semiconductor substrate. As is well known, these layers can be deposited by chemical vapor deposition (CVD) or physical vapor deposition (PVD). In a conventional thermal CVD process, reactive gases are supplied to the substrate surface where heat-induced chemical reactions (homogeneous or heterogeneous) take place to produce a desired film. In a conventional plasma CVD process, a controlled plasma is formed to decompose and/or energize reactive species to produce the desired film. In general, reaction rates in thermal and plasma processes may be controlled by controlling one or more of the following: temperature, pressure, plasma density, reactant gas flow rate, power frequency, power levels, chamber physical geometry, and others. In an exemplary PVD system, a target (a plate of the material that is to be deposited) is connected to a negative voltage supply (direct current (DC) or radio frequency (RF)) while a substrate holder facing the target is either grounded, floating, biased, heated, cooled, or some combination thereof. A gas, such as argon, is introduced into the PVD system, to provide a medium in which a glow discharge can be initiated and maintained. When the glow discharge is started, positive ions strike the target, and target atoms are removed by momentum transfer. These target atoms subsequently condense into a thin film on the substrate, which is on the substrate holder.
In modern semiconductor fabrication, the efficient manufacturing of substrates having devices with increasingly smaller features (e.g., 0.25 .mu.m and smaller) and higher integration density is becoming a growing concern, as the industry seeks to economically produce devices which meet increasingly stringent performance requirements. For example, such devices have features, such as gaps, (with high aspect ratios of, for example, about 7:1 or greater for 0.3 .mu.m feature size devices; where aspect ratio is defined as the height-to-spacing ratio of two adjacent steps) that need to be adequately filled with a uniformly deposited layer in many applications. Being able to deposit uniform films at sufficient deposition rates also is important in producing as many usable substrates with such devices as possible. In addition, it is desirable to increase substrate throughput and yield of usable substrates.
As is well recognized, efficiency issues and device performance problems often arise due to unwanted depositions from repeatedly processing substrates to deposit the desired film. For example, unwanted deposits that have bonded poorly to an underlying chamber component or that have built up on the heater may result in flakes and other particles that fall onto the substrate and cause defects on the substrate, thus reducing substrate yield. For these and other reasons, the chamber must periodically be cleaned (in some applications) with "dry" clean processes, which do not require opening of the chamber. The chamber is cleaned with a less frequent "wet" or preventive maintenance clean, which requires at least partially disassembling the chamber to manually clean with solvents various parts of the chamber. The dry cleaning process may use reactive gas or plasma species to etch unwanted deposits from the chamber components, or may physically bombard particles with plasma species to knock them loose, to be removed by the exhaust system. The wet cleaning process, which may be done in addition or as an alternative to a dry clean, typically involves at least partial disassembly of the chamber, which is then wiped down with solvents. In many processes such as, for example, metal depositions of titanium-containing films, the time required for cleaning the chamber becomes a major factor affecting the deposition system's wafer output. Subsequent to the preventive maintenance clean, the chamber must be reassembled and may be "seasoned", i.e., a number-of deposition cycles must be performed until consistent layers are obtained. Both cleaning procedures take the deposition system out of productive operation, which is inefficient and uneconomic, albeit necessary.
Despite use of wet cleanings, prior titanium nitride processes have been limited in substrate throughput and yield, since the initial 100-300 substrates deposited after the first use of or a preventive maintenance cleaning of the deposition chamber failed to meet acceptable device requirements. For example, a thermal CVD process using vaporized TDMAT has been used for conformally coating titanium nitride (TiN) in a narrow hole or gap. In the TDMAT process, a precursor gas of tetrakis-dimethylamido-titanium, Ti(N(CH.sub.4).sub.2).sub.4, is injected into the chamber (an exemplary chamber is shown in FIG. 1A) through a showerhead 40 at a pressure of about 1 to 9 torr while the pedestal 32 holds the substrate 36 (partially shown) at an elevated temperature of about 360.degree. C. or higher. Thereby, a conductive and conformal TiN layer is deposited on the substrate 36 in a CVD process. The TDMAT process is a thermal process not usually relying upon plasma excitation of the precursor gas. The TDMAT deposition process initially forming the TiN layer may be followed by a second step of plasma treating the deposited TiN layer to remove excessive amounts of carbon which degrades the TiN film's conductivity. The TDMAT gas in the chamber is replaced by an gas mixture of H.sub.2 and N.sub.2 in about a 50:50 ratio at a pressure of about 0.5 to 10 torr, and the RF power source 94 is switched on to create electric fields between the showerhead 40 and the pedestal 32 sufficient to discharge the H.sub.2 :N.sub.2 gas to form a plasma. The hydrogen and nitrogen species in the plasma reduce the carbonaceous polymer in the TiN to volatile byproducts which are exhausted from the system, and the plasma treatment thereby removes the carbon to improve the quality of the TiN film. It is noted that during the thermal phase of the TDMAT process during which the conductive TiN is deposited, the heater 32 is heated and the heat is transferred thence to the wafer 36. In this thermal phase, the exposed portion of the pedestal 32 tends to be at a significantly higher temperature than that of the wafer 36. In particular, to raise the temperature of the wafer 36 to its processing temperature, the temperature of the pedestal 32 is raised to a higher temperature than that of the wafer 36. In this TDMAT process, the processing temperature of the wafer 36 has effectively been about 360.degree. C. while the exposed portion of the pedestal tends to be at a significantly higher temperature of about 425.degree. C. It should also be noted that these prior TiN TDMAT processes were performed at a chamber body temperature (or heat exchange temperature) of about 65.degree. C. TiN films deposited on substrates processed using these prior TDMAT processes did not meet uniformity and/or resistivity specifications for the initial hundreds of substrates. The initial hundreds of processed substrates failing to meet specifications were thus discarded, resulting in the uneconomic waste of both expensive substrates and the time to process these discarded substrates. It is noted that with prior processes, chamber hardware conditions often fluctuated from when the chamber is idling to when the chamber runs a deposition process. The fluctuating chamber hardware conditions resulted in process inconsistencies which was undesirable for depositing films meeting process specifications and repeatability requirements. Accordingly, methods and apparatus for depositing the desired film having good step coverage and meeting uniformity and resistivity specifications while simultaneously increasing substrate throughput and yield in an economic and efficient manner are desired.
In light of the above, improved methods and apparatus are needed for increasing substrate throughput and yield in order to efficiently and economically produce modern semiconductor devices. Optimally, these improved methods and apparatus will be compatible with processing requirements for forming devices with high aspect ratio features.